Nuclear medicine diagnostic apparatus, diagnostic imaging apparatus, and image processing method

ABSTRACT

According to one embodiment, a nuclear medicine diagnostic apparatus includes a counting unit, a region of interest setting unit, a normalization unit, and an image generation unit. The counting unit counts radiation emitted from radioisotopes in an imaging region of an object. The ROI setting unit sets a region of interest (ROI) in the imaging region. The normalization unit determines association between count values and pixel values of display pixels for the ROI in accordance with a distribution of the count values of the display pixels corresponding to the ROI. The image generation unit generates an image of the ROI based on the association between the count values and the pixel values for the ROI.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of No. PCT/JP2013/76235,filed on Sep. 27, 2013, and the PCT application is based upon and claimsthe benefit of priority from Japanese Patent Application No.2012-217895, filed on Sep. 28, 2012, and Japanese Patent Application No.2013-200292, Sep. 26, 2013, the entire contents of all of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a nuclear medicinediagnostic apparatus, a diagnostic imaging apparatus, and an imageprocessing method.

BACKGROUND

Chemicals (blood markers and tracers) containing a radioisotope(hereinafter referred to as an RI) have a property of being selectivelytaken into specific tissues or organs in a living body. A nuclearmedicine diagnostic apparatus uses this property to detect a gamma rayemitted from an RI distributed in a living body with a gamma raydetector provided outside the living body.

A detection result of the gamma rays is used for generation of a nuclearmedicine image that has a brightness distribution corresponding to adose distribution of the gamma rays. Brightness values of the nuclearmedicine image reflect a concentration distribution of an RI in anobject. Accordingly, a user can use the nuclear medicine image for suchpurposes to diagnose functions of organs and the like in the livingbody.

In one method for generating a nuclear medicine image, incident photonsare counted per display pixel based on positional information includedin a detection result of gamma rays, and pixel values (hue, saturationand brightness) of each display pixel are determined by using a colorlook-up table (hereinafter referred to as a LUT) that associates countnumbers and pixel values (color) so as to generate an image.

However, if a predetermined LUT is used for a nuclear medicine imagetaken by whole body photographing, regions with a tendency for high RIconcentration have a high brightness, while regions with a tendency forlow RI concentration, such as a liver, become poor in contrast.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a schematic block diagram illustrating an example of a nuclearmedicine diagnostic apparatus according to one embodiment of the presentinvention;

FIG. 2 is an explanatory view illustrating an example of a nuclearmedicine image of a whole specified imaging region displayed on thedisplay unit;

FIG. 3 is an explanatory view illustrating one of the plurality of theLUTs stored in the storage unit;

FIG. 4 is a flow chart illustrating a procedure for enhancing thevisibility of the partial region in the nuclear medicine image performedby the control unit of the image processing apparatus illustrated inFIG. 1;

FIG. 5 is an explanatory view illustrating an example of setting aregion of interest (ROI) in the specified imaging region;

FIG. 6 is an explanatory view illustrating an example of a normalizedimage of the set ROI;

FIG. 7 is an explanatory view illustrating a method for determiningassociation for ROI according to a first normalization method;

FIG. 8 is an explanatory view illustrating a method for determiningassociation for ROI according to a second normalization method;

FIG. 9A is an explanatory view illustrating a region of a narrow countvalue range being normalization by the first or second normalizationmethod;

FIG. 9B is an explanatory view illustrating a region of a wide countvalue range being normalized by the first or second normalizationmethod;

FIG. 9C is an explanatory view illustrating the region identical to thatof FIG. 9B being normalized by a third normalization method; and

FIG. 10 is an explanatory view illustrating a method for determiningassociation for ROI according to a fourth normalization method.

DETAILED DESCRIPTION

Hereinbelow, a description will be given of a nuclear medicinediagnostic apparatus, a diagnostic imaging apparatus, and an imageprocessing method according to embodiments of the present invention withreference to the drawings.

A diagnostic imaging apparatus and an image processing method accordingto one embodiment of the present invention are applicable to diagnosticimaging apparatuses that perform image processing of medical images. Forexample, the diagnostic imaging apparatus and the image processingmethod are applicable to diagnostic imaging apparatuses, such as anX-ray computed tomography (CT) apparatus, a magnetic resonance imagingapparatus, an ultrasonic diagnostic apparatus, and a nuclear medicinediagnostic apparatus.

Following description discusses an example of using a nuclear medicinediagnostic apparatus as the diagnostic imaging apparatus according tothe present embodiment. The nuclear medicine diagnostic apparatusaccording to the present embodiment is applicable to various apparatuseshaving a gamma ray detector such as a single photon emission computedtomography (SPECT) apparatus and a positron emission tomography (PET)apparatus.

In general, according to one embodiment, a nuclear medicine diagnosticapparatus includes a counting unit, a region of interest setting unit, anormalization unit, and an image generation unit. The counting unitcounts radiation emitted from radioisotopes in an imaging region of anobject. The ROI setting unit sets a region of interest (ROI) in theimaging region. The normalization unit determines association betweencount values and pixel values of display pixels for the ROI inaccordance with a distribution of the count values of the display pixelscorresponding to the ROI. The image generation unit generates an imageof the ROI based on the association between the count values and thepixel values for the ROI.

FIG. 1 is a schematic block diagram illustrating an example of a nuclearmedicine diagnostic apparatus 10 according to one embodiment of thepresent invention.

The nuclear medicine diagnostic apparatus 10 has a gamma ray detector11, a data collection unit 12, and an image processing apparatus 13.Note that the image processing apparatus 13 may be connected to the datacollection unit 12 so that data can be transmitted to and received fromthe data collection unit 12. It is not necessary, therefore, to providethe image processing apparatus 13 in the same room or building as thenuclear medicine diagnostic apparatus 10.

The gamma ray detector 11 is controlled by the image processingapparatus 13 to detect a gamma ray emitted from an RI in a specifiedimaging region of an object.

When a SPECT apparatus is used as the nuclear medicine diagnosticapparatus 10, the gamma ray detector 11 is configured to detect a gammaray emitted from an RI, such as technetium, which is contained inchemicals administered to an object. As the gamma ray detector 11, ascintillator-type detector and a semiconductor-type detector may beused.

The gamma ray detector 11 constructed with the scintillator-typedetector has a collimator for setting an angle of incidence of a gammaray, scintillators that emit a momentary flicker upon incidence of acollimated gamma ray, a light guide, a plurality of photomultipliertubes which are two-dimensionally arrayed for detecting the lightemitted from the scintillators, an electronic circuit for scintillators,and the like. For example, the scintillator is made of thalliumactivated sodium iodide NaI (Tl).

Whenever an event of gamma ray incidence occurs, the electronic circuitfor scintillators generates incident positional information (positionalinformation) and intensity information of the gamma ray on a detectionsurface formed from the plurality of photomultiplier tubes based on anoutput of the plurality of the photomultiplier tubes. The electroniccircuit for scintillators also outputs the generated information to thedata collection unit 12. The positional information may be theinformation on two-dimensional coordinates on the detection surface. Oralternatively, the detection surface may virtually be divided in advanceinto a plurality of subdivisions (hereinafter referred to as primarycells) (e.g., divided into 1,024×1,024 primary cells), and in this case,the positional information may be information indicating which primarycell has received incidence of a gamma ray.

The gamma ray detector 11 constructed with the semiconductor-typedetector has a collimator, a plurality of semiconductor elements forgamma ray detection (hereinafter referred to as semiconductor elements)which are two-dimensionally arrayed for detecting a collimated gammaray, an electronic circuit for semiconductors, and the like. Forexample, the semiconductor elements may be made of CdTe and CdZnTe(CZT).

Whenever an event of gamma ray incidence occurs, the electronic circuitfor semiconductors generates positional information and intensityinformation based on an output of the semiconductor elements, andoutputs the generated information to the data collection unit 12. Thepositional information indicates which semiconductor element, among aplurality of the semiconductor elements (e.g., 1,024×1,024 elements),has received incidence of a gamma ray.

When a PET apparatus is used as the nuclear medicine diagnosticapparatus 10, the gamma ray detector 11 serves to detect a gamma rayemitted from an RI, such as fluorodeoxyglucose (FDG), contained inchemicals administered to an object. In this case, a scintillator-typedetector and a semiconductor-type detector may also be used as the gammaray detector 11. The scintillator-type detector and thesemiconductor-type detector are similar in configuration to those in thecase where the SPECT apparatus is used as the nuclear medicinediagnostic apparatus 10.

When a PET apparatus is used as the nuclear medicine diagnosticapparatus 10, a plurality of detecting elements that constitute thegamma ray detector 11 are arranged, for example, inside a detector coverin a hexagonal or ring shape so as to surround a periphery of an object.Note that the layout of the plurality of the detecting elements is notlimited to a ring-shaped arrangement, but other arrangements such asdual-head arrangement may be adopted. In this arrangement, two detectorseach including a plurality of detecting elements arrayed on a flat platemay face each other across an object while being held rotatably aroundthe object. The plurality of the detecting elements may also beconfigured to be arrayed like a multilayer ring so that an image betweenadjacent layers may be obtained.

More specifically, the gamma ray detector 11 is controlled by the imageprocessing apparatus 13 to detect a gamma ray emitted from an RI in aspecified imaging region of an object and to output positionalinformation and intensity information in every event. The positionalinformation is at least one of the information that indicates theposition of the primary cell that received incidence of a gamma ray andthe information on two-dimensional coordinates on the detection surface.The following description discusses an example in which the gamma raydetector 11 outputs as the positional information the informationindicating an incident position of a gamma ray on the detection surface.

The data collection unit 12 collects an output of the gamma ray detector11, for example, in a list mode. In the list mode, gamma ray detectionpositional information, gamma ray intensity information, informationindicating a relative position of the gamma ray detector 11 and anobject (including a position, an angle and the like of the gamma raydetector 11), and detected time of a gamma ray are collected in everyevent of gamma ray incidence.

The image processing apparatus 13 has a display unit 21, an input unit22, a storage unit 23, a network connection unit 24, and a control unit25 as shown in FIG. 1.

For example, the display unit 21 is made up of a general display outputdevice, such as a liquid crystal display and an organic light emittingdiode (OLED) display. The display unit 21 displays a variety ofinformation such as nuclear medicine diagnosis images under the controlof the control unit 25.

For example, the input unit 22 is formed from a general input device,such as a keyboard, a touch panel and a numeric key pad, and outputs acontrol input signal corresponding to user operation on the control unit25.

The storage unit 23 may include a CPU readable storage medium such as amagnetic or optical recording medium or a semiconductor memory. Some orall of the programs and data in the storage medium may be downloadedthrough an electronic network. The storage unit 23 stores count valuesof respective display pixels and two or more kinds of color look-uptables (LUTs) that associate the count values and pixel values under thecontrol of the control unit 25.

The network connection unit 24 implements various protocols forinformation communication in accordance with the configuration of anetwork 30. The network connection unit 24 connects the image processingapparatus 13 with other electrical apparatuses through the network 30 incompliance with these various protocols. Here, the network 30 refers toa general information communication network using electric communicationtechniques. The network 30 includes wireless/wired LANs such ashospital-based LANs and Internet networks, as well as telephonecommunication line networks, optic fiber communication networks, cablecommunication networks, and satellite communication networks.

An image server 31 is a server included, for example, in a picturearchiving and communication system (PACS) for long-term storage ofimages. The image server 31 stores nuclear medicine images generated inthe nuclear medicine diagnostic apparatus 10. The image server 31 alsostores medical images generated in other modalities such as an X-raycomputed tomography (CT) apparatus 32, a magnetic resonance imaging(MRI) apparatus 33, and an X-ray diagnostic apparatus 34 connectedthrough the network 30. The network 30 is also connected to an externaldatabase 35 that stores, for example, human body atlas data.

The control unit 25 is made up of a CPU, and a storage medium includinga RAM and a ROM. In accordance with a program stored in the storagemedium, the control unit 25 controls processing operation of the imageprocessing apparatus 13.

The CPU of the control unit 25 loads an image processing program storedin a storage medium such as a ROM and data necessary for executing theprogram to a RAM. The CPU then executes processing for enhancingvisibility of a partial region of a nuclear medicine image in accordancewith the program.

The RAM of the control unit 25 provides a work area which temporarilystores the program to be executed by the CPU and the data thereof. Thestorage medium such as the ROM of the control unit 25 stores a start-upprogram and an image processing program of the image processingapparatus 13, and also stores various data necessary for executing theseprograms. The storage medium such as the ROM may include a CPU readablestorage medium such as a magnetic or optical recording medium and asemiconductor memory. Some or all of the programs and data in thestorage medium may be downloaded through an electronic network.

As illustrated in FIG. 1, the image processing program enables the CPUof the control unit 25 to function at least as a count allocation unit41, an image data acquisition unit 42, a region of interest (ROI)setting unit 43, a normalization unit 44, and an image generation unit45. These units 41 to 45 use necessary work areas of the RAM astemporary storage of data. Note that these units for achieving functionsmay be implemented by hardware logic such as a circuit without using theCPU.

The count allocation unit 41 receives from the gamma ray detector 11incident positional information of a gamma ray emitted from a specifiedimaging region. The count allocation unit 41 then associates theincident position in the specified imaging region with display pixels ofthe display unit 21, and allocates (distributes) count values, eachobtained by counting the incident gamma ray in terms of the number ofphotons, to respective display pixels based on the incident positionalinformation, so that an image of the whole specified imaging region isdisplayed.

More specifically, when a SPECT apparatus is used as the nuclearmedicine diagnostic apparatus 10, the count allocation unit 41 acquiresat least positional information and intensity information from the datacollection unit 12. By using a pulse-height discriminator, the countallocation unit 41 extracts only an event that has specified intensityand also extracts only an event that has energy in a specified energywindow. Based on the positional information of the extracted events, thecount allocation unit 41 allocates the count values to the respectivedisplay pixels so that an image of the whole specified imaging region isdisplayed.

When a PET apparatus is used as the nuclear medicine diagnosticapparatus 10, the count allocation unit 41 extracts a combination inwhich an incident time difference in gamma rays (a difference indetection time between a pair of annihilation gamma rays) is in aspecified time window width (for example, in 1 ns or less) and incidentenergies of the pair of the annihilation gamma rays are both within aspecified energy window width. Based on list mode data (coincidencecounting information) of the extracted combination, the count allocationunit 41 allocates count values to the respective display pixels so thatan image of the whole specified imaging region is displayed.

FIG. 2 is an explanatory view illustrating an example of a nuclearmedicine image of a whole specified imaging region displayed on thedisplay unit 21. FIG. 3 is an explanatory view illustrating one of theplurality of the LUTs stored in the storage unit 23. In the presentembodiment, a pixel value refers to at least one of hue, brightness, andchroma. The pixel value (color value) described in the LUTs is a numericvalue to specify at least one of the hue, brightness, and chroma.

The image generation unit 45 receives information on respective countvalues of the display pixels allocated by the count allocation unit 41so that the whole specified imaging region is displayed. By using thereceived count values, the image generation unit 45 calculates pixelvalues of the respective display pixels based on one of the LUTs (forexample, an LUT set as a default LUT to be used unless otherwisespecified by the user) stored in the storage unit 23 to generate anuclear medicine image of the whole specified imaging region. The imagegeneration unit 45 also displays the generated image on the display unit21 (see FIG. 2).

For example, when the count values of the whole specified imaging regionare in the range from a minimum value “sig_min” to a maximum value“sig_max”, the image generation unit 45 calculates pixel values of therespective display pixels in accordance with the count values of therespective display pixels so that the minimum value “sig_min” and themaximum value “sig_max” respectively correspond to a minimum value“col_min” and a maximum value “col_max” of the pixel values (colorvalues) in the LUT (see FIG. 3).

However, if the pixel values of the respective display pixels in thenuclear medicine image of the whole specified imaging region aredetermined by using one LUT as illustrated in FIG. 2, only the regionswith a tendency for high RI concentration have high brightness, whileregions with a tendency for low RI concentration, such as the liver,become poor in contrast. FIG. 3 illustrates one example of the countvalues of a region with a tendency for low RI concentration being in therange from a minimum value “reg_min” to a maximum value “reg_max,” whichis much narrower than the range from “sig_min” to “sig_max.” In thiscase, a range of the LUT from a minimum value “raw_min” to a maximumvalue “raw_max” that correspond to the range from the minimum value“reg_min” to the maximum value “reg_max” also becomes narrow. As aresult, an image of a region within this range becomes low in contrast.

Accordingly, in order to enhance visibility of a partial region in thespecified imaging region, the nuclear medicine diagnostic apparatus 10according to the present embodiment is configured to change associationbetween count values and display pixels of the partial region inaccordance with a distribution of the count values of the partialregion.

First, a basic procedure for enhancing the visibility of a partialregion in a nuclear medicine image is briefly described.

FIG. 4 is a flow chart illustrating a procedure for enhancing thevisibility of the partial region in the nuclear medicine image performedby the control unit 25 of the image processing apparatus 13 illustratedin FIG. 1. In FIG. 4, reference numerals with a character S attachedthereto refer to steps of the flow chart.

FIG. 5 is an explanatory view illustrating an example of setting aregion of interest (ROI) 51 in the specified imaging region. FIG. 6 isan explanatory view illustrating an example of a normalized image of theset ROI 51.

This procedure starts at the moment when a nuclear medicine image of thespecified imaging region is generated by the image generation unit 45.

First, in step S1, the image data acquisition unit 42 acquires a nuclearmedicine image of a specified imaging region generated by the imagegeneration unit 45. The image data acquisition unit 42 also acquires amedical image generated by another modality such as an X-ray CT scannerand an MRI apparatus, if necessary, from the image server 31 through thenetwork 30.

Next, in step S2, the ROI setting unit 43 sets an ROT 51 in thespecified imaging region automatically, semi-automatically or manuallyin response to an instruction by a user through the input unit 22 (seeFIG. 5). FIG. 5 illustrates an example of setting the liver as the ROI51.

Next, in step S3, the normalization unit 44 changes pixel values ofdisplay pixels in accordance with a distribution of pixel values of thedisplay pixels corresponding to the ROI. More specifically, for example,the normalization unit 44 determines association between count valuesand pixel values of display pixels for the ROI 51 in accordance with adistribution of the count values of the display pixels corresponding tothe ROI 51 with use of an LUT stored in the storage unit 23.

Next, in step S4, the image generation unit 45 generates an image of theROI based on the pixel values of the display pixels changed by thechanging unit. More specifically, for example, the image generation unit45 generates a normalized image of the ROI 51 by calculating pixelvalues of the respective display pixels corresponding to the ROI 51based on the association between the count values and the pixel valuesfor the ROI 51, and displays the generated image on the display unit 21(see FIG. 6). In the present embodiment, the normalized image refers toan image generated based on the association between count values andpixel values of display pixels for the ROI 51 which is determined inaccordance with the distribution of the count values of the displaypixels corresponding to the ROI 51.

It is to be noted that the image generation unit 45 may superimposinglydisplay (fuse and display) a normalized image of the ROI 51 and amedical image generated by another modality on the display unit 21.

Through the above procedure, the visibility of the partial region in thespecified imaging region can be enhanced.

Now, methods for setting the ROI 51 are described in detail.

There are mainly two methods for setting the ROI 51: a method involvinguse of only the nuclear medicine images; and a method involving use ofmedical images generated by another modality, such as an X-ray CTscanner and an MRI apparatus.

First, the method involving use of only the nuclear medicine images willbe described. In this method, the image data acquisition unit 42acquires the nuclear medicine image of the specified imaging regiongenerated by the image generation unit 45 in step S2 of FIG. 4.

In the case of automatically setting the ROI 51, information on aspecified area (such as the liver, for example) to be set as the ROI 51is given to the ROI setting unit 43 as instructed by the user throughthe input unit 22 in advance or by initial setting. The ROI setting unit43 compares the nuclear medicine image of the specified imaging regionwith human body atlas data stored in the external database 35, andthereby sets the region of the specified area as the ROI 51. In the caseof automatically setting the ROI 51, the ROI setting unit 43 may segmentthe region of the specified area in a full-automatic mode to set the ROI51.

In the case of semi-automatically setting the ROI 51, the ROI settingunit 43 first receives operation of specifying a target area to be setas the ROI 51 from the user through the input unit 22. Examples of thespecifying operation include, for example, the user clicking one pointwithin the region of a target area to be set as the ROI 51 in a nuclearmedicine image of a specified imaging region while viewing andconfirming the nuclear medicine image displayed on the display unit 21.Once the user specifies the target area to be set as the ROI 51 byclicking one point within the region of a specified area, and thespecifying operation is accepted, the ROI setting unit 43 then segmentsthe region of the area, and thereby sets the ROI 51.

In the case of manually setting the ROI 51, the ROI setting unit 43 setsthe ROI 51 in response to an ROI arrangement instruction by the userthrough the input unit 22 or a block definition instruction by draggingof a mouse.

Next, a method for using medical images generated by another modality,such as an X-ray CT scanner and an MRI apparatus, will be described. Inthis method, the image data acquisition unit 42 acquires the nuclearmedicine image of the specified imaging region generated by the imagegeneration unit 45 in step S2 of FIG. 4, and also acquires a medicalimage generated by another modality, such as an X-ray CT scanner and anMRI apparatus, from the image server 31 through the network 30. Themedical image includes at least an image of a region set as the ROI 51.The following description discusses an example of the medical image thatincludes a specified imaging region.

In the case of automatically setting the ROI 51, the information on aspecified area (such as the liver, for example) to be set as the ROI 51is given to the ROI setting unit 43 as instructed by the user throughthe input unit 22 in advance or set by initial setting, as in the caseof the method involving use of only the nuclear medicine image.

The ROI setting unit 43 compares a medical image of a specified imagingregion generated by another modality with the human body atlas datastored in the external database 35 so as to extract the region of aspecified area. The ROI setting unit 43 then sets a region in thenuclear medicine image corresponding to the region of the specified areaextracted from the medical image as the ROI 51. Moreover, in the case ofautomatically setting the ROI 51, the ROI setting unit 43 may segmentthe region of the specified area in the medical image generated byanother modality in the full-automatic mode and set a region of thenuclear medicine image corresponding thereto as the ROI 51.

In the case of semi-automatically setting the ROI 51, the ROI settingunit 43 first receives operation of specifying a target area to be setas the ROI 51 in the medical image from the user through the input unit22. Examples of the specifying operation include, for example, the userclicking one point within the region of a target area to be set as theROI 51 in a medical image of a specified imaging region while viewingand confirming the medical image displayed on the display unit 21 as inthe case of the method involving use of only the nuclear medicineimages. Once the user specifies a target area to be set as the ROI 51 byclicking one point within the region of a specified area in the medicalimage generated by another modality, and the specifying operation isaccepted, the ROI setting unit 43 then segments the region of the areain the medical image, and sets a region in the nuclear medicine imagecorresponding thereto as the ROI 51.

In the case of manually setting the ROI 51, the ROI setting unit 43receives an ROI arrangement instruction for the medical image generatedby another modality through the input unit 22 operated by the user or ablock definition instruction generated by dragging of a mouse.Consequently, a region in the nuclear medicine image corresponding tothe instructed region is set as the ROI 51.

It is to be stated that the method for setting the ROI 51 is not limitedto the methods disclosed. For example, in the case of using a medicalimage generated by another modality, once the user specifies a targetarea to be set as the ROI 51 in the medical image by clicking one pointwithin the region of a specified area in the medical image generated byanother modality, and the specifying operation is accepted, a positionin the nuclear medicine image corresponding to the point indicated byclicking operation may be obtained, and a region including the positionin the nuclear medicine image may be segmented to set the ROI 51.Moreover, once the user specifies a target area to be set as the ROI 51in the nuclear medicine image by clicking one point within the region ofa specified area in the nuclear medicine image, and the operation ofspecifying the target area to be set as the ROI 51 in the nuclearmedicine image is accepted, a position in the medical image generated byanother modality corresponding to the point indicated by clickingoperation may be obtained, a region including the position in themedical image may be segmented, and a region in the nuclear medicineimage corresponding to the segmented region in the medical image may beset as the ROI 51.

Now, methods (hereinafter referred to as normalization methods) fordetermining association between count values and pixel values for theROI 51 (hereinafter referred to as association for ROI) are described indetail.

There are mainly four normalization methods as shown below. In thefollowing description, a minimum value of the count values of thedisplay pixels corresponding to the ROI 51 is defined as “reg_min,” anda maximum value thereof is defined as “reg_max.” A minimum value and amaximum value in a pixel value range (color range) of an LUT applied forgenerating an image of a whole specified imaging region (see FIG. 2) aredefined as “col_min” and “col_max,” respectively.

FIG. 7 is an explanatory view illustrating a method for determiningassociation for ROI according to a first normalization method.

The first normalization method is a method for determining associationfor ROI in accordance with the range from the minimum value “reg_min” tothe maximum value “reg_max” of the count values of the display pixelscorresponding to the ROI 51.

In this method, the normalization unit 44 calculates a normalized countvalue “nor_val” by using Formula (1):

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack & \; \\{{nor\_ val} = {{\frac{{value} - {reg\_ min}}{{reg\_ max} - {reg\_ min}} \cdot \left( {{col\_ max} - {col\_ min}} \right)} + {col\_ min}}} & (1)\end{matrix}$

In Formula (1), “value” represents a count value of each display pixeland “nor_val” represents a normalized (corrected) count value. Formula(1) is a formula to directly change a pixel value (color value) of theLUT pointed by the count value of each display pixel. By using Formula(1), “nor_val” of the count values “value” of all the display pixelscorresponding to the ROI 51 is calculated. As a result, the range fromthe minimum value “reg_min” to the maximum value “reg_max” of the countvalues of the display pixels corresponding to the ROI 51 and the pixelvalue range of the LUT applied in generating an image of the wholespecified imaging region (see FIG. 2) can be made to correspond to eachother (see FIG. 7).

According to the first normalization method, a nuclear medicine image ofthe ROI 51 with enhanced contrast and high visibility can be generatedby using the same LUT as that for the specified imaging region.

FIG. 8 is an explanatory view illustrating a method for determiningassociation for ROI according to a second normalization method.

The second normalization method is a method for determining associationfor ROI in accordance with an average “reg_ave” and a variance “reg_σ”of the count values of the display pixels corresponding to the ROI 51.

In this method, the normalization unit 44 obtains a normalized countvalue “nor_val” by using Formula (2):

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack & \; \\{{nor\_ val} = {{\frac{{value} - {reg\_ ave}}{reg\_\sigma} \cdot {tar\_\sigma}} + {tar\_ ave}}} & (2)\end{matrix}$

In Formula (2), “tar_ave” represents an arbitrarily specified givenaverage value, and “tar_σ” represents an arbitrarily specified givenvariance. Formula (2) is a formula for correcting the count value ofeach display pixel to a value suitable for the same LUT as that for thespecified imaging region. By using Formula (2), “nor_val” of the countvalue “value” of all the display pixels corresponding to the ROI 51 iscalculated. Consequently, the count value “value” of each display pixelcan be corrected to a normalized count value “nor_val,” so that theaverage “reg_ave” and the variance “reg_σ” of the count values of thedisplay pixels corresponding to the ROI 51 are matched with a givenaverage “tar_ave” and a variance “tar_σ” Therefore, by using the sameLUT as that for the specified imaging region and calculating the pixelvalues of the LUT that correspond to the normalized count value“nor_val,” the pixel values of the respective display pixels aredetermined, and a normalized image can be thereby generated.

According to the second normalization method, a nuclear medicine imageof the ROI 51 with enhanced contrast and high visibility can also begenerated by using the same LUT as that for the specified imagingregion.

FIG. 9A is an explanatory view illustrating a region of a narrow countvalue range being normalization by the first or second normalizationmethod, while FIG. 9B is an explanatory view illustrating a region of awide count value range being normalized by the first or secondnormalization method. FIG. 9C is an explanatory view illustrating theregion identical to that of FIG. 9B being normalized by a thirdnormalization method.

The third normalization method is a method for determining associationfor ROI in accordance with an average “reg_ave” and a variance “reg_σ”of the count values of the display pixels corresponding to the ROI 51.This method is different from the second normalization method in thatthe LUT to be used is changed in accordance with the average “reg_ave”and the variance “reg_σ.”

When the count value range of the display pixels corresponding to theROI 51 is narrow as illustrated in FIG. 9A, the range of the LUTcorresponding to this count value range (from a minimum value “raw_min”to a maximum value “raw_max”) is also narrow. In this case, contrast cansufficiently be enhanced by expanding the corresponding range of the LUTby using the first or second normalization method.

However, when the count value range of the display pixels correspondingto the ROI 51 is relatively wide and the corresponding LUT range (fromthe minimum value “raw_min” to the maximum value “raw_max”) is wide asillustrated in FIG. 9B, the contrast is not greatly enhanced even if thecorresponding LUT range is expanded with use of the same LUT by thefirst or second normalization method.

Accordingly, as illustrated in FIG. 9C, the range of the LUT is changedin accordance with a distribution of the count values of the displaypixels corresponding to the ROI 51, and the association for ROI isdetermined with use of the changed LUT. As a result, the contrast of theROI 51 can be enhanced regardless of the count value range of thedisplay pixels corresponding to the ROI 51.

Specifically, when an average of the count values of the display pixelscorresponding to the ROI 51 is “reg_ave” and a variance is reg_σ, thenormalization unit 44 sets a center WL of the LUT as “reg_ave” and awidth WW of the LUT as “A*reg_σ” (provided that A represents a givenvalue).

According to the third normalization method, the LUT range is changed inaccordance with the distribution of the count values of the displaypixels corresponding to the ROI 51, so that a nuclear medicine image ofthe ROI 51 with enhanced contrast and high visibility can be generated.Note that the normalization unit 44 may extract one LUT out of aplurality of LUTs prestored in the storage unit 23 as the LUT for theROI in accordance with the average “reg_ave” and the variance “reg_σ” ofthe count values of the display pixels corresponding to the ROI 51. Theextracted LUT may have a center WL and a width WW closer to “reg_ave”and “A*reg_σ,” respectively.

FIG. 10 is an explanatory view illustrating a method for determiningassociation for ROI according to a fourth normalization method.

The fourth normalization method is a method for correcting the countvalue of each display pixel corresponding to the ROI 51 in accordancewith a ratio between a blood flow rate associated with the ROI 51 and agiven blood flow rate.

In this method, the normalization unit 44 obtains a normalized countvalue “nor_val” by using Formula (3):

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack & \; \\{{nor\_ val} = {\frac{base\_ bv}{tar\_ bv} \cdot {value}}} & (3)\end{matrix}$

In Formula (3), “base_bv” represents a standard blood flow rate of anarea corresponding to the ROI 51, and “tar_bv” represents a given bloodflow rate specified by the user through the input unit 22 or set byinitial setting.

The standard blood flow rate varies in each organ. Depending on theblood flow rate, RI concentration tendency varies and the count valuevaries either. Accordingly, when an organ region is set as the ROI 51,the standard blood flow rate “base_bv,” which is different by area, isnormalized by using Formula (3) based on the ratio to a given blood flowrate.

For example, a case of setting four regions: a heart region, a headregion, a liver region, and a kidney region, as the ROI 51 isconsidered. In this case, by using, for example, the standard blood flowrate of the liver as the given blood flow rate “tar_bv,” the head andthe kidney which are high in brightness value can be observed at thesame brightness level as the liver region. A value of a specific area orany other values may be used as “tar_bv.”

According to the fourth normalization method, a nuclear medicine imageof the ROI 51 with enhanced contrast and high visibility inconsideration of the blood flow rate of the ROI region 51 can begenerated by using the same LUT as that for the specified imagingregion.

The nuclear medicine diagnostic apparatus 10 according to the presentembodiment can enhance the visibility of a partial region of a nuclearmedicine image. Accordingly, when an imaging region includes a regionwith a tendency for low RI concentration, for example, setting theregion with a tendency for low RI concentration as the ROI 51 can makeit easy to observe an image of such region. Therefore, the nuclearmedicine diagnostic apparatus 10 according to the present embodiment canincrease a detection rate of lesion parts which have been hard to detectuntil now and can also enhance diagnostic speed.

Moreover, the nuclear medicine diagnostic apparatus 10 can reduceinterobserver errors occurring when multiple observers observe anidentical image as well as intraobserver errors occurring when oneobserver observes one image multiple times. Accordingly, appropriatediagnosis regardless of experiences of an observer and the like can besupported.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

For example, a diagnostic imaging apparatus according to one embodimentof the present invention may be an apparatus which can adaptively changeassociation between count values and pixel values of display pixelscorresponding to an arbitrary region in accordance with a distributionof the count values of the display pixels of the region. Therefore,although in the aforementioned embodiment, a nuclear medicine diagnosticapparatus has been described as the diagnostic imaging apparatusaccording to one embodiment of the present invention, modalities usableas the diagnostic imaging apparatus may include an X-ray CT scanner, amagnetic resonance imaging apparatus, and an ultrasonic diagnosticapparatus, without being limited to the nuclear medicine diagnosticapparatus. Furthermore, the medical images handled by the diagnosticimaging apparatus are not limited to nuclear medicine images. Forexample, perfusion images generated by the X-ray CT scanner may also behandled by the diagnostic imaging apparatus.

What is claimed is:
 1. A nuclear medicine diagnostic apparatus,comprising processing circuitry configured to perform operations,including to: count radiation emitted from radioisotopes in an imagingregion of an object; set a region of interest (ROI) in the imagingregion; determine association between count values of the countedradiation and pixel values of display pixels for the ROI in accordancewith a distribution of the count values of the display pixelscorresponding to the ROI, wherein the operation to determine associationincludes to determine association between count values and pixel valuesof display pixels for a whole region including the ROI such that a rangeof the count values of display pixels corresponding to the whole region,ranging from a minimum value to a maximum value, corresponds to aspecified pixel value range; generate an image of the ROI based on theassociation between the count values and the pixel values for the ROI;for the ROI, correct the count values of the respective display pixelscorresponding to the ROI such that an average and a variance of thecount values of the display pixels corresponding to the ROI match with aspecified average and a specified variance, respectively; and whereinthe operation to generate the image of the ROI includes calculating,with use of the corrected count values, the pixel values of therespective display pixels corresponding to the ROI based on theassociation between the count values and the pixel values for the wholeregion.
 2. The nuclear medicine diagnostic apparatus according to claim1, wherein the processing circuitry is configured to set a regioncorresponding to the ROI in a medical image of the object generated byanother modality, and to set the ROI based on the set region.
 3. Thenuclear medicine diagnostic apparatus according to claim 1, wherein theprocessing circuitry is configured to superimposingly display thegenerated image of the ROI and a medical image of the object generatedby another modality on a display.
 4. The nuclear medicine diagnosticapparatus according to claim 1, wherein the processing circuitry isconfigured to display on a display the image of the ROI generated basedon the association between the count values and the pixel values for theROI.
 5. A nuclear medicine diagnostic apparatus, comprising processingcircuitry configured to: count radiation emitted from radioisotopes inan imaging region of an object; set a region of interest (ROI) in theimaging region; providing a table associating count values of thecounted radiation and pixel values of display pixels used for the ROI;change an average and the range of the pixel values in the table inaccordance with an average and a variance of the count values of thedisplay pixels corresponding to the ROI, respectively; determine anassociation between the count values and the pixel values of the displaypixels corresponding to the ROI by using the changed table; and generatean image of the ROI by calculating the pixel values of the respectivedisplay pixels corresponding to the ROI based on the determinedassociation between the count values and the pixel values.
 6. Thenuclear medicine diagnostic apparatus according to claim 5, wherein theprocessing circuitry is configured to display on a display the image ofthe ROI generated based on the association between the count values andthe pixel values for the ROI.
 7. The nuclear medicine diagnosticapparatus according to claim 5, wherein the processing circuitry isconfigured to set a region corresponding to the ROI in a medical imageof the object generated by another modality, and to set the ROI based onthe set region.
 8. The nuclear medicine diagnostic apparatus accordingto claim 5, wherein the processing circuitry is configured tosuperimposingly display the generated image of the ROI and a medicalimage of the object generated by another modality on a display.
 9. Animage processing method, comprising: counting radiation emitted fromradioisotopes in an imaging region of an object; setting a region ofinterest (ROI) in the imaging region; determining association betweencount values of the counted radiation and pixel values of display pixelsfor the ROI in accordance with a distribution of the count values of thedisplay pixels corresponding to the ROI; and generating an image of theROI based on the association between the count values and the pixelvalues for the ROI, wherein the determining association includesdetermining association between count values and pixel values of displaypixels for a whole region including the ROI in such a manner that arange of the count values of display pixels corresponding to the wholeregion, ranging from a minimum value to a maximum value, corresponds toa specified pixel value range, and for the ROI, correcting the countvalues of the respective display pixels corresponding to the ROI in sucha manner that an average and a variance of the count values of thedisplay pixels corresponding to the ROI match with a specified averageand a specified variance, respectively, and wherein generating the imageof the ROI comprises calculating, with use of the corrected countvalues, the pixel values of the respective display pixels correspondingto the ROI based on the association between the count values and thepixel values for the whole region.
 10. An image processing method,comprising: counting radiation emitted from radioisotopes in an imagingregion of an object; setting a region of interest (ROI) in the imagingregion; and providing a table associating count values of the countedradiation and pixel values used for display pixels for the ROI; changingan average and the range of the pixel values in the table in accordancewith an average and a variance of the count values of the display pixelscorresponding to the ROI, respectively, and determining an associationbetween the count values and the pixel values of the display pixelscorresponding to the ROI by using the changed table; and generating animage of the ROI, wherein generating the image comprises calculating thepixel values of the respective display pixels corresponding to the ROIbased on the determined association between the count values and thepixel values.